As used herein, the term “molten metal” means any metal or combination of metals in liquid form, such as aluminum, copper, iron, zinc and alloys thereof. The term “gas” means any gas or combination of gases, including argon, nitrogen, chlorine, fluorine, freon, and helium, which are released into molten metal.
Known pumps for pumping molten metal (also called “molten-metal pumps”) include a pump base (also called a housing or casing), one or more inlets to allow molten metal to enter a pump chamber (an inlet is usually an opening in the pump base that communicates with the pump chamber), a pump chamber, which is an open area formed within the pump base, and a discharge, which is a channel or conduit communicating with the pump chamber (in an axial pump the pump chamber and discharge may be the same structure or different areas of the same structure) leading from the pump chamber to the molten metal bath in which the pump base is submerged. A rotor, also called an impeller, is mounted in the pump chamber and is connected to a drive shaft. The drive shaft is typically a motor shaft coupled to a rotor shaft, wherein the motor shaft has two ends, one end being connected to a motor and the other end being coupled to the rotor shaft. The rotor shaft also has two ends, wherein one end is coupled to the motor shaft and the other end is connected to the rotor. Often, the rotor shaft is comprised of graphite, the motor shaft is comprised of steel, and these two shafts are coupled by a coupling, which is usually comprised of steel.
As the motor turns the drive shaft, the drive shaft turns the rotor and the rotor pushes molten metal out of the pump chamber, through the discharge, which may be an axial or tangential discharge, and into the molten metal bath. Most molten metal pumps are gravity fed, wherein gravity forces molten metal through the inlet and into the pump chamber as the rotor pushes molten metal out of the pump chamber.
Molten metal pump casings and rotors usually employ a bearing system comprising ceramic rings wherein there are one or more rings on the rotor that align with rings in the pump chamber (such as rings at the inlet (which is usually the top of the pump chamber and bottom of the pump chamber) when the rotor is placed in the pump chamber. The purpose of the bearing system is to reduce damage to the soft, graphite components, particularly the rotor and pump chamber wall, during pump operation. A known bearing system is described in U.S. Pat. No. 5,203,681 to Cooper, the disclosure of which is incorporated herein by reference. As discussed in U.S. Pat. Nos. 5,591,243 and 6,093,000, each to Cooper, the disclosures of which are incorporated herein by reference, bearing rings can cause various operational and shipping problems and U.S. Pat. No. 6,093,000 discloses rigid coupling designs and a monolithic rotor to help alleviate this problem. Further, U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat. No. 4,169,584 to Mangalick, U.S. Pat. No. 5,203,681 to Cooper and U.S. Pat. No. 6,123,523 to Cooper (the disclosures of the afore-mentioned patents to Cooper, insofar as such disclosures are not inconsistent with the teachings of this application, are incorporated herein by reference) all disclose Molten metal pumps. Furthermore, U.S. patent application Ser. No. 10/773,102 to Cooper, filed on Feb. 4, 2004, which is now U.S. Pat. No. 7,402,276 and entitled “Pump With Rotating Inlet” discloses, among other things, a pump having an inlet and rotor structure (or other displacement structure) that rotate together as the pump operates in order to alleviate jamming. The disclosure of this copending application, insofar as such disclosures are not inconsistent with the teachings of this application, is incorporated herein by reference.
The materials forming the components that contact the molten metal bath should remain relatively stable in the bath. Structural refractory materials, such as graphite or ceramics, that are resistant to disintegration by corrosive attack from the molten metal may be used. As used herein “ceramics” or “ceramic” refers to any oxidized metal (including silicon) or carbon-based material, excluding graphite, capable of being used in the environment of a molten metal bath. “Graphite” means any type of graphite, whether or not chemically treated. Graphite is particularly suitable for being formed into pump components because it is (a) soft and relatively easy to machine, (b) not as brittle as ceramics and less prone to breakage, and (c) less expensive than ceramics.
Three basic types of pumps for pumping molten metal, such as molten aluminum, are utilized: circulation pumps, transfer pumps and gas-release pumps. Circulation pumps are used to circulate the molten metal within a bath, thereby generally equalizing the temperature of the molten metal. Most often, circulation pumps are used in a reverbatory furnace having an external well. The well is usually an extension of a charging well where scrap metal is charged (i.e., added).
Transfer pumps are generally used to transfer molten metal from the external well of a reverbatory furnace to a different location such as a ladle or another furnace. Examples of transfer pumps are disclosed in U.S. Pat. No. 6,345,964 B1 to Cooper, the disclosure of which, insofar as such disclosures are not inconsistent with the teachings of this application, is incorporated herein by reference, and U.S. Pat. No. 5,203,681.
Gas-release pumps, such as gas-injection pumps, circulate molten metal while releasing a gas into the molten metal. In the purification of molten metals, particularly aluminum, it is frequently desired to remove dissolved gases such as hydrogen, or dissolved metals, such as magnesium, from the molten metal. As is known by those skilled in the art, the removing of dissolved gas is known as “degassing” while the removal of magnesium is known as “demagging.” Gas-release pumps may be used for either of these purposes or for any other application for which it is desirable to introduce gas into molten metal. Gas-release pumps generally include a gas-transfer conduit having a first end that is connected to a gas source and a second submerged in the molten metal bath. Gas is introduced into the first end and is released from the second end into the molten metal. The gas may be released downstream of the pump chamber into either the pump discharge or a metal-transfer conduit extending from the discharge, or into a stream of molten metal exiting either the discharge or the metal-transfer conduit. Alternatively, gas may be released into the pump chamber or upstream of the pump chamber at a position where it enters the pump chamber. A system for releasing gas into a pump chamber is disclosed in U.S. Pat. No. 6,123,523 to Cooper. Another gas-release pump is disclosed in a co-pending U.S. patent application filed on Feb. 4, 2004 and entitled “Gas-Release System for Molten Metal Pump” to Paul V. Cooper, the disclosure of which that is not inconsistent with the teachings of this application is incorporated herein by reference.
A problem with known pumps is that that they include a superstructure that is positioned above the molten metal bath when the pump is in use. The pump motor, among other things, rests upon the superstructure. The superstructure is positioned above the molten metal bath by one or more support posts connected to the pump base. The support posts must, therefore, be attached to the superstructure to support it, and if more than one support post is used, each must maintain the superstructure at about the same height relative the pump base in order to keep the superstructure level. Each support post is attached to the superstructure by a post clamp that typically has a portion (such as a flange) that connects to the superstructure and another portion that connects to the support post.
The primary methods of locating and connecting each support post to the superstructure at the same relative height have been to machine a groove or hole in each post at the same location. If a groove is formed, it is formed in the outer surface of the support post, and the groove mates with a corresponding lip on a support post clamp. The clamp also includes a lower flange that connects to the superstructure and the flange and the lip support the weight of the superstructure. Such a system is shown in U.S. Pat. No. 5,203,681.
Another known method for locating a support post relative a superstructure is by the use of a through-bolt hole. Utilizing this system, a hole, or bore, is drilled through each support post at the same location on each post. A cylindrical, preferably two-piece post clamp having an aperture formed on either side, receives an end of the support post and a bolt is passed through the apertures and a bore (also called a through bolt hole) in the support post. Lower flanges on the post clamp are connected to the superstructure and the bore in the support post supports the weight of the superstructure. Such a system is shown in U.S. Pat. No. 5,203,681.
A problem with these known methods of connecting a support post to a superstructure is the time required to precisely locate and machine the grooves or through bolt holes at the same location on each support post so that the superstructure is level when the pump is used. Another problem is that the weight of the superstructure is supported by grooves or bores in the support posts, which are usually made of relatively soft graphite. Supporting the weight of the superstructure in this manner can cause the support posts to crack or break.